Ice-cream is a partly-frozen foam, incorporating fat globules, ice crystals and air bubbles. The conventional approach to the production of partially frozen water mixtures, such as ice-cream and ice-cream type products requires inter alia that the ice-cream mixture is simultaneously frozen and mechanically whipped, to produce ice crystals and air bubbles, respectively. This usually involves a ‘barrel freezer’, which is a scraped-surface, tubular heat exchanger in which the batch freezing process takes 10-15 minutes. There are rotating blades inside the barrel that keep the ice scraped off the freeze surface and there are usually internal vanes/fins to aid whipping and incorporation of air.